Felton went down at the 18th hole at the Whistling Straits course in Sheboygan while playing in a celebrity match, according to The Associated Press.
The actor was playing for the European celebrity team, one day before the start of the tournament that pits U.S. golf pros against their European counterparts.
Photos posted by the AP showed a dazed-looking Felton being helped to his feet, and a distressed-looking Felton being transported on a golf cart.
As of early Friday ET there was no update on Felton’s medical condition.
The collapse happened just one day after the actor celebrated his 34th birthday.
"33 years done – good lord it’s been so much fun getting here," Felton wrote on Twitter to mark the milestone, although his math was a bit off. "yet, somehow, I still feel the best is yet to come – thank you for your love, support & sense of humour – let’s keep a good thing going – to the next 33 xx."